ARP send request to wrong ip

[flycatr]

How to reproduce:

1. Run a container and connect to external PPTP server. Make sure client successfully connected (ppp0 interface appear when typing ifconfig). Check container ip (e.g 172.17.0.2)
2. Stop container.
3. Repeat step 1. This time PPTP client failed to connect. Check container ip (e.g 172.17.0.3)

Analysis:
From tcpdump (tcpdump -i vethxxxx), arp is sending request to previous ip172.17.0.2, but the current container ip is 172.17.0.3. Below is an excerpt from tcpdump output:

....
12:12:03.565472 IP 172.17.0.3.34739 > au1.vyprvpn.com.1723: Flags [.], ack 189, win 119, options [nop,nop,TS val 1746395 ecr 3707168897], length 0
12:12:03.565906 IP 172.17.0.3 > au1.vyprvpn.com: GREv1, call 30446, seq 1, length 36: LCP, Conf-Request (0x01), id 1, length 22
12:12:03.617655 ARP, Request who-has 172.17.0.2 tell 172.17.42.1, length 28
12:12:04.614870 ARP, Request who-has 172.17.0.2 tell 172.17.42.1, length 28
12:12:05.614837 ARP, Request who-has 172.17.0.2 tell 172.17.42.1, length 28
....

Workaround:
Restart docker service before running again container - service docker restart

[aluzzardi]

Thanks @flycatr for the bug report.

Could you provide some additional information (docker version etc), as described in:
https://github.com/docker/docker/blob/master/CONTRIBUTING.md#reporting-issues

[flycatr]

Here are more informations (my machine is ubuntu 14.04):

root@mail:~# uname -a
Linux mail.testmachine 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

root@mail:~# docker version
Client version: 1.2.0
Client API version: 1.14
Go version (client): go1.3.1
Git commit (client): fa7b24f
OS/Arch (client): linux/amd64
Server version: 1.2.0
Server API version: 1.14
Go version (server): go1.3.1
Git commit (server): fa7b24f

root@mail:~# docker -D info
Containers: 2
Images: 24
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Dirs: 28
Execution Driver: native-0.2
Kernel Version: 3.13.0-32-generic
Operating System: Ubuntu 14.04.1 LTS
Debug mode (server): false
Debug mode (client): true
Fds: 15
Goroutines: 14
EventsListeners: 0
Init Path: /usr/bin/docker
WARNING: No swap limit support

... and here are how my arp cache looks like during the process:

Before running any container.

Address                  HWtype  HWaddress           Flags Mask            Iface
128.199.128.1            ether   00:00:5e:00:02:64   C                     eth0

Start a container, and run pptp client. Client connected to ppp server.

Address                  HWtype  HWaddress           Flags Mask            Iface
172.17.0.3               ether   0e:f1:cf:dc:1e:f5   C                     docker0
128.199.128.1            ether   00:00:5e:00:02:64   C                     eth0

Re-run again (stop & start the same container).

Address                  HWtype  HWaddress           Flags Mask            Iface
172.17.0.3                       (incomplete)                              docker0
172.17.0.4               ether   1a:d1:2c:b8:69:4e   C                     docker0
128.199.128.1            ether   00:00:5e:00:02:64   C                     eth0

Something is very wrong if arp result is showing incomplete word. It should not be there in the first place.

Here is my ip neigh result:

root@mail:~# ip neigh
172.17.0.3 dev docker0  FAILED
172.17.0.4 dev docker0 lladdr 1a:d1:2c:b8:69:4e REACHABLE
128.199.128.1 dev eth0 lladdr 00:00:5e:00:02:64 REACHABLE

[flycatr]

This is my docker command:

docker run -i -t --name chromecast_1 --rm --device=/dev/ppp --cap-add=NET_ADMIN chromecast_img pppd call au1.vyprvpn dump debug

[aluzzardi]

@flycatr: Can you retry out of master?

[flycatr]

It works! Problem solved. Thank you!!!!

$ docker -v
Docker version 1.2.0-dev, build 84d9fd3

Here are my arp results:

Before running any container

Address                  HWtype  HWaddress           Flags Mask            Iface
128.199.128.1            ether   00:00:5e:00:01:65   C                     eth0

Container first run

Address                  HWtype  HWaddress           Flags Mask            Iface
172.17.0.18              ether   02:42:ac:11:00:12   C                     docker0
128.199.128.1            ether   00:00:5e:00:01:65   C                     eth0

The same container, stop and start again

Address                  HWtype  HWaddress           Flags Mask            Iface
172.17.0.18              ether   02:42:ac:11:00:12   C                     docker0
128.199.128.1            ether   00:00:5e:00:01:65   C                     eth0

Good job @aluzzardi & friends ! 👍